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秦啸.分布式交互系统中连续媒体的延迟一致性模型.软件学报,2002,13(6):1029-1039
分布式交互系统中连续媒体的延迟一致性模型
Delayed Consistency Model for Distributed Interactive Systems with Real-Time Continuous Media
投稿时间:2001-03-31  修订日期:2001-08-16
DOI:
中文关键词:  一致性维护  交互式对象  连续媒体  分布式系统
英文关键词:consistency maintenance  interactive object  continuous media  distributed systems
基金项目:Supported in part by an ARC (Australia Research Council) Large Grant No.A00000711 (澳大利亚研究委员会大型项目部分资助)
作者单位
秦啸 内布拉斯加-林肯大学,计算机科学与工程系,内布拉斯加,林肯,68588-0115,美国 
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中文摘要:
      随着多媒体和网络技术的发展,分布式交互系统被广泛应用.在这种系统中,多个客户端通过局域或广域网交互连接.为使响应时间短,本地节点产生的操作立即在本地执行,并广播到其他远程节点执行.在该系统中,一致性维护是一个关键问题,而文献中研究的一致性问题几乎都是基于不连续媒体的.通过一个实例,指出连续媒体中的一种不一致问题.虽然该问题可以通过绝对一致模型解决,但绝对一致模型应用在广域网中将导致长响应时间.为解决绝对一致模型中响应时间过长的问题,提出了延迟一致性模型(简称为DCM模型).在DCM中,如果节点i产生了作用于对象x上的操作,该操作到达远程节点后强行延迟一段时间并要求在统一规定的时间执行.通过该方法,对象x在其他远程节点上的状态将最终保持一致.DCM很灵活,因为不同的对象可以有不同的强行延迟时间.如果分布式交互系统建立在实时网络上,这种强行延迟时间将成为实时通信中实时消息调度的重要参数.
英文摘要:
      The advanced multimedia and high-speed networks make distributed interactive systems more promising and practical. These systems are distributed systems, which allow many clients located in different locations to concurrently explore and interact with each other. The systems can be built either in the localarea network (LAN), or the wide area network (WAN), such as the Internet. Operations issued at one site are immediately executed at the local sites for a good response time, and are propagated to other sites. One of the challenging issues raised in the systems is consistency maintenance. Such issue in the discrete interactive media has been studied in many literatures. However, the consistency maintenance scheme for discrete interactive media is not suitable for continuous media domain. This paper illustrates a consistency problem in continuous interactive media by a simple example. The absolute consistency model, a strong requirement, is suitable for LAN and results in a bad responsiveness in WAN. To make themodel more practical for WAN, a new consistency model, named delayed consistency model (DCM), is proposed. In this model, if an operation on an object x is issued at site i, every site is required to execute the operation at a specified time. The essential idea behind the proposed model is that other sites are enforced to update the state at a certain amount of time later than site i does. Thus, other sites will finally view the same state of x as that of site i. The DCM model is flexible, since it is unnecessary for all sites to have the identical delayed time. In case that the system is based on a real-time network, another advantage of the model is providing the real-time network scheduling with important timing parameters.
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